A hydrogen passivation strategy for the electrocatalytic chlorine evolution reaction on metal-organic frameworks: a theoretical insight.

Abstract

The chlorine evolution reaction (CER) is a crucial solution for treating chlorine-containing wastewater, a type of wastewater generated during the chemical production process. Electrocatalysts applied are mainly dimensionally stable anodes (DSAs) such as precious metals and their oxides. In order to reduce the amounts of rare metals in the catalysts and to improve the catalytic performance, a hydrogen-passivated transition metal site strategy based on a metal-organic framework, TM3(THT)2 (TM = Mn, Fe, Co, Ni, Tc, Ru, Rh, Pd, Re, Os, Ir, Pt), was proposed to force the CER to proceed at the sulfur (S) site. With the help of density functional theory (DFT), the CER process at the transition metal (TM) site and the S site in TM3(THT)2 before and after H passivation has been systematically researched. The results revealed that, for the same catalyst, the catalytic performance for the CER after passivation was significantly improved compared with that before the passivation. The Gibbs free energy of Re3(THT)2 was -0.085 eV after the H passivation. Meanwhile, at an external voltage of 0 V, the theoretical overpotential of the oxygen evolution reaction (OER) was obviously greater than that of the CER. Therefore, excellent activity and selectivity for the CER were demonstrated using the H-passivated Re3(THT)2. Electronic structure analysis revealed that the natural origin of the weak adsorption was the overlap of the p orbital of the S site with the p orbital of Cl, and the overlap area was smaller than the overlap of the d orbital of Re with the p orbital of Cl. To obtain excellent catalytic performance for the CER, the electro zcatalyst should activate Cl while minimizing the adsorption of Cl as much as possible. The strategy of the hydrogen passivation of highly active sites proposed in this article may be an effective means to improve the catalytic performance of metal-organic frameworks for the CER.